1. Field of the Invention
The present invention relates to a prefilled syringe and, more particularly, to a pre-filled syringe having a non-gasket structure requiring no lubricant such as silicone oil, which is substantially free from eluting material and low in sliding resistance between a syringe barrel and a plunger.
2. Description of the Prior Art
There have been known so-called prefilled syringes or a syringe ready for administration of a liquid medicine to a patient, comprising a barrel previously filled with a liquid medicine. The administration can be done with such a syringe by removing a hermetic seal from a tip of the barrel and then fitting a hypodermic needle over the tip of the barrel. The barrel filled with a liquid medicine is generally sealed at one end by a rubber gasket and at the other end or a needle-connecting portion by a rubber plate.
However, such prefilled syringes of the prior art employing such sealing members have a serious problem for use in infusion since the rubber plate and rubber gasket allow compounding agents such as sulfur and vulcanization accelerators or impurities contained therein to elute in the liquid medicine during storage of the syringes.
In order to overcome such disadvantages of the prefilled syringe of the prior art, in examined Japanese Utility model publication No. 55-32602 it has been proposed to use a prefilled syringe comprising a barrel of glass in combination with sealing member coated or covered with a thin film of a plastic material other than fluorine-contained resin at all the surfaces to be in contact with a liquid medicine. However, such a syringe has a problem in slidability of the resin coated sealing members. This problem may be overcome by use of gaskets made of fluorine contained resin, but fluorine contained resin causes other problems; for example in liquid-tightness and airtightness when the resin coated sealing members are used in combination with the glass barrels.
For these reasons, disposable syringes widely used today are those employing a barrel made of plastics. When using the plastic barrels in combination with a gasket made of plastics other than fluorine-contained resin, it is necessary to apply silicone oil as a lubricant on sliding surfaces of the gasket since the slidability of the gasket decreases with increase in liquid-tightness and airtightness between the gasket and barrel. However, silicone oil is a foreign substance for the medicament to be administered and causes particulate contamination of the medicament.
To solve such problems, it has been proposed in examined Japanese utility model publication No. 5-34669 to use a gasket of which all the surfaces to be in contact with a liquid medicine and to be slid on the inner wall of the barrel are covered with a thin film selected from the group consisting of polytetrafluoroethylene film, ethylene-tetra fluoroethylene copolymer film and ultra-high-molecular weight polyethylene film and which has a length of a contacting surface between a peripheral portion of the gasket and the inner wall of the barrel being limited within a certain range.
Although the gasket disclosed in examined publication No. 5-34669 is sufficient when used for ordinary syringes, they causes problems in liquid-tightness and airtightness when used for prefilled syringes. For example, if the plunger is pressed hardly during storage, the liquid medicine may leak out from the syringe, different from the close contact between the elastic gasket and inner wall of the barrel.